Propene Polymerization Using Homogeneous MAO-Activated Metallocene Catalysts: Me2Si(Benz[e]lndenyI)2ZrClu'MAO vs. Me2Si(2-Me-Benz[e]lndenyI)2ZrClu'MAO
STEPHAN JUNGLlNG,t ROLF MULHAUPT,b UDO STEHLlNG/ HANS-HERBERT BRINTZINGER/ DAVID FISCHER/ and FRANZ LANGHAUSER3 'Institut fOr Makromolekulare Chemie and Freiburger Materialforschungszentrum der Albert-Ludwigs-Universitat Freiburg, 0-79104 Freiburg, Germany; 2Fakultat fOr Chemie, Universitat Konstanz, 0-78434 Konstanz, Germany; and 3BASF AG Abteilung ZKP, 0-67056 Ludwigshafen, Germany
SYNOPSIS Propene was polymerized at 40°C and 2-bar propene in toluene using methylalumoxane (MAO) activated rac-Me2Si(Benz[elIndenyl)2ZrCI2 (BI) and rac-Me2Si(2-Me Benz[elIndenyl)2ZrCl2 (MBI). Catalyst BI/MAO polymerizes propene with high activity to afford low molecular weight polypropylene, whereas MBI/MAO is less active and produces high molecular weight polypropylene. Variation of reaction conditions such as propene concentration, temperature, concentration of catalyst components, and addition of hydrogen reveals that the lower molecular weight polypropylene produced with BI/MAO results from chain transfer to propene monomer following a 2,1-insertion. A large fraction of both me tallocene catalyst systems is deactivated upon 2,1-insertion. Such dormant sites can be reactivated by H2-addition, which affords active metallocene hydrides. This effect of H2- addition is reflected by a decreasing content of head-to-head enchainment and the formation of polypropylene with n-butyl end groups. Both catalysts show a strong dependence of activity on propene concentration that indicates a formal reaction order of 1. 7 with respect to propene. MBI/MAO shows a much higher dependence of the activity on temperature than BI/MAO. At elevated temperatures, MBI/MAO polymerizes propene faster than BI/ MAO. Keywords: propene. polymerization. zirconocene • methylalumoxane • chain transfer· end groups· hydrogen. 2,1-insertion
INTRODUCTION is possible to control molecular weight, stereo regularities, and comonomer incorporation without In recent years, versatile generations of Ziegler sacrificing the narrow molecular weight distribu Natta catalysts based upon MAO-activated metal tions. In spite of these improvements in catalyst 1 3 locenes have been developed. - Polypropylene can technology, there is still much to be learned about be produced with high catalyst activity, isotacticity, the elementary steps in olefin polymerization. and molecular weight. As a result of the uniform Small changes in the ligand structure of the catalytically active sites ("single site catalyst"), it metallocene can lead to polyolefins with greatly varied properties. Our research is aimed at better understanding of the main factors controlling * To whom all correspondence should be addressed at Univ the behavior of the two metallocenes rac-Me2Si ersitiit Freiburg, Institut fUr Makromolekulare Chemie, Stefan (Benz[e]Indenyl}2ZrCI2 (BI) and rac-Me2Si(2-Me Meier-Str. 31, 79104 Freiburg, Germany. Benz[e]IndenylhZrCI2 (MBI), see Scheme 1. The catalyst BI/MAO was previously shown to poly-
1305 1306
rac-M~Si(BeDz[e]Indcnyl~ (BI) rac-~Si(2-Me-Benz[e]IndenylhZrCl2' (MBI)
Scheme 1.
merize propene with high activity producing low Figure 3 shows the plot of the polymerization rates molecular weight polymer, while MBI/MAO showed [kgPP I (mol Zr X h) ] that correspond to the activity the opposite behavior, i.e., lower catalyst activity maxima seen in Figures 1 and 2 vs. propene on a 4 5 and higher polypropylene molecular weight. • double logarithmic scale. The reaction order of the polymerization rate with respect to propene con centration is 1.7 for both catalysts. This is signifi RESULTS AND DISCUSSION cantly higher than expected for the model of mono mer-metal7r-complex formation followed by the in sertion as the rate-determining step. Propene polymerization was performed in a reactor Similar results concerning the relationship be at 0.5 to 6-bar propene pressure in toluene. The tween polymerization rate and monomer concentra MAO Itoluene solution was injected into the reactor tion have been observed by Fink et al. for metallo and saturated with propene. Polymerization was cene IMAO catalysts, e.g., a reaction order in pro started by injecting a solution of the metallocene in pene of 1.2 to 1.4 for Me2Si(IndhZrC12/MAO and diluted MAO Itoluene. The temperature was con Me2C(Cp)(Flu)ZrC12/MAO.6 This was attributed trolled within ±O.I°C, and pressure was maintained to additional reactions that were not specified in by feeding propene. detail. Siedle et al. also reported higher orders of reaction for the system CP2ZrC12/MAO 11-hexene.7 Influence of Propene Concentration Due to the heterogeneous character of the suspen sion polymerization of propene in toluene, it is con Table I shows the effect of propene concentration ceivable that mass transfer is the main factor con on the maximum catalyst activity at 40°C. Activities trolling the activity of the system. Figure 4 shows the of both catalysts, measured as kgPP I (mol Zr X moll variation of the catalyst activity for MBI/MAO with L Pr X h), increase strongly with propene concen propene concentration when the propene pressure is tration. Figures 1 and 2 show the time dependence increased in steps from 1 bar to 1.5 and 2 bar, and of the catalyst activity for the two metallocenes for decreased again to 1.5 and 1 bar. Catalyst activity in different propene pressures. For BI/MAO, catalyst creases and decreases parallel to propene concentra activity increases within the first 10 to 20 min fol tion. The catalyst activity at 2 bar and 80 min is almost lowed by a slow deactivation. The maxima of the identical to the activity at 80 min ofthe corresponding activity I time curves shift to higher activities with system (run #82) polymerizing propene with 2 bar increasing propene concentration. For MBI/MAO, propene over the entire reaction time. The reversibility maximum activity is reached shortly after injection of the activity Ipropene concentration dependence in of the metallocene IMAO solution. At propene pres dicates that equilibria involving the active species are sures of 2 bar or less, almost no deactivation is de responsible for this effect rather than mass transfer, tected. At higher pressures, the polymerization has because the latter would be expected to depend on the to be quenched after 10 min due to stirring problems previous history of the system. associated with extremely low bulk density of the Incomplete heat transfer in the polymer I catalyst resulting polypropylene. particles could be another reason for the observed 1307
activity increase. MAO-activated metallocenes are known to show increasing activity with rising po lymerization temperatures. Localized "overheating"
C':>l..Cc.oc-:l~ "
MO~LC~ ~tt5t.OO~ 00"'''''''c-i~LDcD as generally observed for polymers produced at LDll':llOc.oc.o "
p = kpropagation [m] ( 1) l:t)C"Ir-IC"I-.::t' OOC"l..-tC'J 1""""I-.::t'O':IOM r-4~O':IO n ktransfer + ktransfer monomer [M] cicicic-ic
Equation 1 assumes that only one propene mol ecule is involved in the propagation step, and that the observed higher reaction order of the rate of po lymerization is caused by a change in the number of currently active sites and that the sites active for chain transfer and propagation are identical. Plot ting 1 j P n vs. 1 j [ M] separates the relative rate con stants for the (3- H -elimination with and without I':: • monomer participation. The relative rate constants ::> 0 ~z without monomer paticipation (ktransferj kpropagation) 1308
activity
80000
x
~ a. 60000 ...... J o E x
~ N 40000 o E ~ ...... a. a. ...0> 20000
od-____L- ____L- __~ ____~ ____~ _____L ____ _L ____ ~ ____~_J o 20 40 80 80 100 120 140 180 180 time [min] Figure 1. Catalyst activities of Me2Si(Benz[eJlndhZrCI2/MAO at different propene con centrations: [ZrJ = 1 X 10-6 mol/L , [AI]/[ZrJ = 20,000, toluene, 40°C, total pressure 0.5- 4 bar. (a) [Prj = 0.18 mol/L, (b) [Prj = 0.42 mol/L, (c) [Prj = 0.91 mol/L, (d) [Prj = 2.02 mol/L. are 1.6 X 10-4 mol/L for the catalyst BI/MAO and agree well with the results found at 50°C for the same 1.5 X 10-4 mol/L for MBI/MAO. The relative rate metallocenes.5 This explains the low molecular weight constants for chain transfer with monomer partic observed for the polypropylene produced by BI/MAO ipation (ktransfer monomer! !lpropagation) are 1.3 X 10 -3 for by the high rate of chain transfer to the monomer BI/MAO and 1.4 X 10-4 for MBI/MAO. These data for the metallocene BI. The methyl groups in the 2-
100000
activity 6A~ e ~ BOOOO .r:
)( a.~ j ...J -::::. 0 80000 E
)(
~ N 0 40000 .5- ...... a. a. oo .)(. 20000 V
30 40 50 eo time [min] Figure 2. Catalyst activities of Me2Si(2-Me-Benz[ e Jlnd)2ZICI2/MAO at different propene concentrations: [ZrJ = 1 X 10-6 mol/L , [AIJ/[ZrJ = 20,000, toluene, 40°C, total pressure 0.5-6 bar. (a) [Prj = 0.18 mol/L, (b) [Prj = 0.42 mol/L, (c) [Prj = 0.91 mol/L, (d) [Prj = 2.02 mol/L, (e) [Prj = 3.3 mol/L. 1309
rate of polymerization yields E act = 54 kJ /mol for MBI/MAO and E act = 28 o kJ /mol for BI/MAO. The higher activation energy for MBI/MAO is compensated by a more favorable .D ~ entropy. The activation energy for MBI/MAO is ..M 100 o surprisingly high in comparison to the values for N BI/MAO and Cp2ZrCI2/MAO (Eact = 37 kJ /mol '0 a BI .... cr· measured under similar conditions) .11 The Arrhenius plot for the polymer molecular "- 11. weight is shown in Figure 9. In the case of MBI/ 11. MAO, producing the higher molecular weight poly 10 ...... 0.·· WBI • .. propylene, one finds a higher difference Eact (Polym.) ....0 -E act (Termin.) = -40 kJ/mol than for BI/MAO with E act (Polym.) - E act (Termin.) = -16 kJ /mol. However, these values indicate the presence of dif ferent types of chain transfer in comparison to the 0.3 0.5 1 3 5 aspecific, oligomer-yielding Cp2ZrCI2/MAO with E act c(propene) [mol/L] (Polym.) - E act (Termin.) = - 51 kJ /molY Figure 3. Rate of polymerization for MBI/MAO and BI/MAO at different propene concentrations; logarith mic plot; MBI = Me2Si(2-Me-Benz[eJInd)2ZrCI2' BI End Group Analysis 6 = Me2Si(Benz[eJInd)2ZrCI2; [ZrJ = 1 X 10- mol/L, [AIJ/ The typical polymer end groups, found in low mo [ZrJ = 20,000, toluene, 40°C, total pressure 0.5-6 bar; rp m lecular polypropylenes produced by metallocene = k' X [propenel ; log(rp) = m X log([propene]) + log(k'); catalysts such as Cp2ZrCI2/MAO or Et(lndH )2 m = 1.7; the maximum rate of polymerization correspond 4 ing to Figures 1 and 2 is used, the error bar covers the ZrCI2/MAO, are the vinylidene group resulting from results of five polymerization runs, the largest uncertainty {3-I-I-elimination and the n-propyl group formed by is due to the error in the metallocene concentration. insertion of propene into the resulting Zr-hydrideP Figure 10 shows the IH-NMR spectra of the ole finic region for the polymers produced with BI/ position at the benz [ e ] indenylligand in MBI seem MAO (a) and MBI/MAO (b). The vinylidene end to be able to suppress this type of transfer. group at 4.74 and 4.66 ppm is the only end group found for MBI/MAO (b). But for BI/MAO (a), in addition to the vinylidene end group signals, a Influence of Temperature more intense signal at 5.45 ppm is seen. For BI/ Figure 7 shows the activity-time profile as a function MAO, the 13C-NMR spectrum of the olefinic region of temperature for the two metallocene /MAO cat ofthe polymer shows signals at 129.4 and 124.3 ppm. alyst systems at constant propene pressure. At 60°C We assign these signals observed for polymer pro catalyst activity increases steeply within the first duced with BI/MAO to a 2-butenyl end group minutes of the polymerization, followed by a slow (MeHC=CH-CH2-), which results from 2,1- deactivation to roughly 50% over 3 h for both cat propene insertion followed by {3- H -elimination.13 alysts. At 40°C, only BI/MAO shows this type of For run #89 (BI/MAO, 40°C, 0.91 mol/L pro behavior, while MBI/MAO deactivates much pene, Table I), one expects about 90% of the chain slower. At 20°C, both metallocenes polymerize with termination to occur with monomer participation, almost constant activity over several hours. Dou as estimated from the corresponding chain transfer bling the zirconocene concentration of MBI/MAO rate constants determined above. The intensity of from 1 to 2 JLmol/L does not have any significant the IH-NMR olefinic proton signal at 5.45 ppm ac impact on catalyst activity, and polymer properties counts for 60-70% of the total intensity observed as can be seen in Table II. for all olefinic end groups. This indicates that this MBI/MAO shows a very strong increase of ac new chain termination pathway is a {3-hydride tivity with temperature, becoming faster than BI/ transfer to a coordinated propene, following a 2,1- MAO at 60°C. This agrees with Spaleck's observa insertion, as shown in Scheme 2. The 2-methyl group tions that catalyst activity for MBI/MAO is higher in MBI/MAO seems to be able to suppress this than for BI/MAO at 70°C in liquid propene.4 The pathway, explaining the higher molecular weight of Arrhenius plot (Fig. 8) of the maximum activities polymer produced with MBI/MAO. 1310
30000 r------.-----.------,-----~------~----_.------~----~ 2.0
',;i' loB " 25000 .. 1.6 ~ II...... :I '0 1.4 '0 activity ! S 20000 1'1 .2 1.2 ...... "...... 1'1 '0 15000 1.0 II. ! "1'1 ...... 0 O.B II. "II. 1'1 ; 10000 ,.------'1 I~ II. 0.6 Po I propene conoentration I ..0 ... Po ~ 0.4 -... 5000 .." 0.2
o~----~----~----~------~----~----~----~~--~ 0.0 o 20 40 60 BO 100 120 140 160 time [min] Figure 4. Catalyst activities of Me2Si(2-Me-Benz[ejInd)2ZICI2/MAO at different propene concentrations; step-wise change of propene pressure during one polymerization run: [Zrj = 1 X 10-6 mol/L , [Alj/[Zr j = 20,000, toluene, 40°C, total pressure 1, 1.5, 2 bar. After each propene pressure change activity measurement was omitted for about 15 min to allow for stabilization of the reaction conditions (dotted line).
The lH-NMR of polypropylene produced by BI/ group. This group could arise from an isomerization MAO at low propene concentrations or higher tem of the vinylidene end group forming the thermo perature shows a third olefinic signal at 5.18 ppm dynamically favored vinylene group with internal that might be due to a Me2C=CH-CH- end double bond.14
100 .------,------,------,------, 165.0
99 162.5
9B 160.0 MBI 97 157.5 M ...... 96 155.0 E S 152.5 9 95 II S ... 94 150.0 BI 93 147.5
92 145.0
91 142.5
90 '--______.J.- ______-"- ______~ ______-' 140.0 o 234 o(propene) [mol/L] Figure 5. Dependence of polymer melting point and tacticity on propene con centration for MBI/MAO and BI/MAO, MBI = Me2Si(2-Me-Benz[ejInd)2ZrCI2, BI = Me2Si(Benz[ejInd)2ZrCI2. [Zrj = 1 X 10-6 mol/L, [Alj/[Zrj = 20,000, toluene, 40°C, total pressure 0.5-6 bar. 1311
JOOr------.------,------r------, 0.8% 2,1-units to be incorporated into the polymer. This would mean that the catalytic site is deacti 250 vated by an 2,1-insertion taking place. Such dormant sites are reactivated when a 1,2-insertion or chain transfer to propene occurs. Scheme 3 shows possible ~ 200 '0 pathways for the reactivation of Zr-2,1-units...... a For run #89 (BI/MAO, 40°C, 0.91 mol/L pro ~ 150 pene, Table I) , one can estimate from the statistical chain length of the polymer and the amount of 2,1- 100 insertions that chain transfer to propene from a Zr- 2,1-unit is about 10 times slower than 1,2-insertion into a Zr-2,1-unit. 50 o BI ~ OL______-L ______~ ______L______~ Polymerization in the Presence of Hydrogen o 2 J 4 o(propene) [mol/L] Formation of dormant sites after 2,1-insertions has Figure 6. Dependence of polymer molecular weight on been shown to be important for heterogeneous propene concentration for MBI/MAO and BI/MAO, catalysts 15 as well as for zirconocene /MAO / propene MBI = Me2Si(2-Me-Benz[ejInd)2ZrCI2' BI = Me2Si systems 13.16 by the analysis of polymer end groups (Benz[ejInd)2ZrCI2' [Zrj = 1 X 10-6 mol/L , [AIll[Zrj when hydrogen was added to the polymerization. = 20,000, toluene, 40°C, total pressure 0.5-6 bar. Table III shows the effect of addition of 0.35 bar H2 to the system for the metallocene catalysts BI/ Elimination following 2,1-insertion as the main MAO and MBI/MAO. Polymerization activity for chain termination pathway for BI/MAO requires BI/MAO is increased by 38%, while for MBI/MAO that a significant part of the catalytic sites has a an activity increase of 17% is found. Adding H2 re 2,1-unit as the last-inserted unit if one assumes duces 2,1-units in the polymer to one-third for both chain transfer from a 2,1-unit to be of the same order metallocenes. This reduction of incorporated 2,1- as from an 1,2-unit. However 13C-NMR shows only units is paralleled by an increase of n-propyl- and
100000 IIBI-o '''-'' aoUnt,. / ...... ,.... 80000 ... ~ ..-- ~ .." ...... 0.. ... - ...... J .. -----.-- Ci 60000 ...------.. .-...... a....-.... E .... '\ " N ~ Ci 40000 5 ...... 0.. 0..... ~ 20000
O~ ____~ ____L- __~L_ __~ ____~ ____~ ____-L ____ -L ____ ~~ o 20 40 60 80 100 120 140 160 180 time [min]
Figure 7. Activities of MBI/MAO and BI/MAO at different temperatures: [Zrj = 1 X 10-6 moljL , [Alj/[Zrj = 20,000, toluene, total pressure 2 bar. MBI = Me2Si(2-Me Benz[ejInd)2ZrCI2, BI = Me2Si(Benz[ejlnd)2ZrCI2' (a) T = 20°C, (b) T = 40°C, (c) T = 60°C. 1312
: ~~c:.c ~t-t.- ~~r--: Figure 8. Arrhenius plot for the activity of MBI/MAO c-.i ~,....; c-.i""';""'; ~ ~!""'I and BI/MAO; log (activity) vs. l/temp [AI] = 20 X 10-3 mol/L, toluene, total pressure 2 bar. 0 = BI/MAO, [Zr] = 1 X 10-6 mol/L; 0 = MBI/MAO, [Zr] = 1 X 10-6 mol/ o "" L; 0 = MBI/MAO, [Zr] = 2 X 10-6 mol/L. n-butyl-polymer end groups as can be seen in Figure 11 for BIjMAO. The n-propyl and n-butyl-polymer end groups have the same intensity, while isopropyl end groups 000 000 could hardly be detected within the limits ofthe 13C_ 000 000 r-oo 000 20 <00 .... ""00 .... NMR measurement. This shows that most metal "" .... 00 ""'" locenes have a 2,1-inserted propene as the last unit of the polymer chain, if one assumes the rates of chain transfer to H2 from a Zr-2,1-unit and a Zr- 1,2-unit to be of the same magnitude. This seems 16 to be realistic for the small hydrogen molecule. ,17 :2 The fraction of metallocenes deactivated by 2,1- ...* N units can be estimated by studying the effect of hy- 1000 r---~---r--~~--~--~--~ ..-. '0 El ...... 110 ~ 100 000 000 000 "" .... <0 "" .... <0 "" .... <0 ;3 -N... ---0 .-< .-< .-< .-< .-< .-< -5 10 L-__~ __~ __-L __ -L __ ~ __~ .3 2.9 3.0 3.1 3.2 3.3 3.4 3.5 9 1 1 10 l[ T- [K- ] Figure 9. Arrhenius plot for polymer molecular weights for BIjMAO and MBI/MAO; log (activity) vs. l/temp, [Al] = 20 X 10-3 mol/L, toluene, total pressure 2 bar. 0 = BI/ I': • 6 ;:l 0 MAO, [Zr] = 1 X 10- mol/L; 0 = MBI/MAO, [Zr] = 1 ..::Z 6 6 X 10- mol/L; 0 = MBI/MAO, [Zr] = 2 X 10- mol/L. 1313 * * a * * b (ppm) Figure 10. Polymer IH-NMR-spectra for different metallocenes region of olefinic end groups; [AI] = 20 X 10-3 mol/L, toluene, 2 bar. (a) Me2Si(Benz[e]Ind)2ZrCI2/MAO, [Zr] = 1 X 10-6 mol/L, (b) Me2Si(2-Me-Benz[e]Ind)2ZrCI2/MAO, [Zr] = 2 X 10-6 mol/L. Signals marked with * are due to solvent C2D2C14 • drogen on catalyst activity and polymer microstruc to a threefold catalyst activity increase for the sys ture. The chain transfer from a Zr-2,I-unit to H2 is tems with hydrogen, if the major fraction of the me about two times faster than 1,2-insertion of propene tallocenes is blocked by 2,1-units. The observed cat into this unit. This can be concluded from the con alyst activity increase by H2 is much lower (38% for centrations of the products of these steps. The in BI/MAO, 17% for MBI/MAO). This phenomenon tensities of signals in the I3C-NMR-spectra due to could be explained either by impurities introduced n-butyl-end groups are two times larger than those by H 2-addition or by questioning the assumption of for 2,I-units in the polymer. Thus, the overall rate the same HTtransfer rate for Zr-2,1- and Zr-l,2- of deblocking 2,I-units either by 1,2-propene inser units or by a lower rate of insertion at the beginning tion or by transfer to hydrogen should be three times of the polymer chain. IS Using the three times higher larger than without H 2-addition. This should lead rate of transfer of 2,I-units into 1,2-units in the CHs I CHs CH2 -CH-P CHs CH3 CH3 I I I \ / H C-CH=CH-CH -CH-P CH-CH-CH -CH-P CH=CH 3 2 .,/'" I 2 I \ M H M H + \ , , \ , , CH2 ... CH ~C~ \ CH2 CH3 CHs Scheme 2. j3-hydrogen transfer from a Zr-2,1-unit to propene. 1314 CHs CHs CHs I I I M-CH2 -CH-CH-CH2 -CH2 -CH-P Scheme 3. Pathways of reactivation of a dormant Zr-2,1-unit. presence of H2 as determined above and the observed ca. 20% for MBIjMAO under the assumption of a catalyst activity increase, one can estimate the por rate of insertion independent of chain length. This tion of Zr-2,1-units to be ca. 40% for BIjMAO and fits to the two times higher probability for 2,1-inser- m-2.1 m-2.1 m mm cPS C C C I P2 P1 I I I mrr Pol-C-C-C-C Po I-C-C-C-C-C-C-P 0 I mm CB6 C r-2.1 C I B2 B1 I I Pol-C-C-C-C-C Po I-C-C-C-C-C-C-P 0 I I C r-2.1 mrrm m-2,i m-2,i r-2,i r-2,i Pi 82 86 P2 mrrm P5 Pi 81 m-2,1 m-2,1 23 22 21 20 19 18 17 16 15 14 (ppm) Figure 11. l3C NMR-spectra of polymers prepared in the absence (a) and presence (b) of hydrogen, region of methyl carbons; for Me2Si(Benz[eJlnd)2ZrCl2/MAO; [ZrJ = 1 X 10-6 moljL, [AlJ/[Zr] = 20,000, toluene, 40°C, 2 bar propene. (a) Without hydrogen, run #89; (b) with 0.35 bar hydrogen, run #103. PI, P2, P5: n-propyl end group signals; B1, B2, B6: n-butyl end group signals; m-2,1: signals of meso-2,1-units; r-2,1: signals of rac-2,1-units. 1315 tion for BI/MAO compared to MBI/MAO. But this leaves the problem that there are almost no isopropyl end group signals detectable in the 13C_NMR.20 CONCLUSION Propene concentration has been shown to be an im portant parameter for MAO-activated homogeneous catalysts based on the metallocenes BI and MBI, influencing catalyst activity, polymer molecular weight, polymer end groups, and even polymer tac ticity and melting temperatures. For BI/MAO, chain transfer to propene from a Zr-2,1-unit controls the molecular weight of the polymer, leading to MeHC=CH-CH2- end groups. Addition of hydrogen to polymerizations with BI/ MAO and MBI/MAO reduces the incorporation of 2,1-inserted propene units into the polymer and leads to n-butyl and n-propyl end groups. This in dicates that a substantial part of the metallocene is blocked by 2,1-units. The introduction of a methyl group in the 2-po sition on the benz [e 1indenylligand in MBI/MAO leads to a higher energy of activation for the poly merization and to a more favorable entropy of ac tivation than that of BI/MAO. The difference be tween the energies of activation for chain propa gation and termination is higher for MBI/MAO than for BI/MAO, as can be expected from the high molecular weight polymer produced by MBI/MAO. EXPERIMENT AL The time dependence of the polymerization activity 00 00 00 00 00 00 was determined by the pressure drop in a thermo 010 00 argon. 99.99% argon (Messer Griesheim GmbH) was purified by passing through BTS-cat alyst (BASF AG) and 0.4 nm molecular sieve. Po lymerization grade propene (BASF AG) was stored over Al(i-Buh/toluene prior to use. 99.999% hy drogen (Messer Griesheim GmbH) was used without further purification. Toluene p.a. (Roth AG) was purified by passing through a column with acidic Al20 3 (Merck AG) and distillation over LiAIH4 fol >:: • lowed by at least 12 h refluxing over Na/K-alloy ::> 0 ~z and fresh distillation prior to use. 1316 The synthesis of the zirconocenes BI and MBI REFERENCES AND NOTES has been described previously.5 The autoclave and pressure buret were washed with a ca. 1 wt % Al(i-Buh/toluene solution at 1. (a) A. Andresen, H.-G. Cordes, J. Herwig, W. Ka minsky, A. Merck, R. Mottweiler, J. Pein, H. Sinn, 60°C. A 10 wt % solution of MAO (8.7 mL) in tol and H.-J. Vollmer, Angew. Chem., 88,689 (1976), uene (WitcoAG Mn = ca. 800 g/mol) was added to Angew. Chem. Int. Ed. Eng., 15,630 (1976); (b) W. 700 mL oftoluene. This solution (600 mL) was can Kaminsky, K. Kiilper, H. H. Brintzinger, and nulated into the evacuated autoclave followed by F. R. W. P. Wild, Angew. Chem., 97, 507 (1985), saturation with propene at the polymerization tem Angew. Chem. Int. Ed. Eng., 24, 507 (1985); (c) K. perature. The above solution (30 mL) was used to Heiland and W. Kaminsky, Makromol. Chem., 193, dissolve 1.23 jlmol of the zirconocene. Twenty min 601 (1992); (d) W. Kaminsky, R. Engehausen, K. utes later, 15 mL of this solution was injected into Zoumis, W. Spaleck, and R. Rohrmann, Makromol. the thermostated, pressurized reactor via a pressure Chem., 193,1643 (1992); (e) W. Kaminsky and A. buret to start the reaction. The concentration is, Noll, Polym. Bull., 31, 175 (1993). thus, 1jlmol/L for the zirconocene, 20 mmol/L Al 2. (a) P. Burger, K. Hortmann, and H.-H. Brintzinger, for MAO, with a ratio AI/Zr = 20000 (total Zr = 6.15 Makromol. Chem. Macromol. Symp., 66, 127 (1993); (b) W. Roll, H.-H. Brintzinger, B. Rieger, and R. Zolk, X 10 -7 mol, total Al = 1.23 X 10 -2 mol). Angew. Chem., 102,339 (1990), Angew. Chem. Int. The reaction was stopped by venting off the pro Ed. Eng., 29, 279 (1990); (c) F. R. W. P. Wild, L. pene and precipitating the polymer in 1 L methanol Zsolnai, G. Huttner, and H.-H. Brintzinger, J. Or with 40 mL 10% aq. HCI and 0.5 g 2,6-di-t-butyl-4- ganomet. Chem., 232, 233 (1982). methyl-phenol (BHT). After stirring the mixture 3. (a) J. A. Ewen, J. Am. Chem. Soc., 106,6355 (1984); overnight, the polymer was filtered off and washed (b) J. A. Ewen, Catalytic Polymerization of Olefins , with methanol and dried at 60°C at reduced pressure T. Keii, K. Soga, Eds., Elsevier, Kodansha, Tokyo, to constant weight. 1986, p. 271; (c) J. A. Ewen, M. J. Elder, R. L. Jones, NMR spectra were recorded from solutions of 40 L. Haspeslagh, J. L. Atwood, S. G. Bott, and K. Rob inson, Makromol. Chem. Macromol. Symp., 48/49, to 110 mg of polymer in 0.4 mL C2D2Cl4 at 400 K by a Bruker ARX 300. IH-NMR spectra were re 253 (1991); (d) J. A. Ewen and M. J. Elder, Makromol. Chem. Macromol. Symp., 66, 179 (1993). corded at 300 MHz with 128 scans, and 13C-NMR 4. (a) W. Spaleck, M. Antberg, J. Rohrmann, A. Winter, spectra at 75.4 MHz with a 30° pulse angle, 3.5 s B. Bachmann, P. Kiprof, J. Behm, and W. A. Herr pulse repetition and 11,111 Hz spectra width, and mann, Angew. Chem., 104, 1373 (1992); Angew. at least 5,000 scans. For the polymers produced in Chem. Int. Ed. Eng., 31, 1347 (1992); (b) W. Spaleck, the presence of hydrogen, 20,000 scans were re F. Kuber, A. Winter, J. Rohrmann, B. Bachmann, M. corded. For the spectrum of the olefinic carbons of Antberg, V. Dolle, and E. F. Paulus, Organometallics, the polypropylene from BI/MAO, 50,000 scans were 13,954 (1994). recorded at 380 K, with the reduced spectra width 5. U. Stehling, J. Diebold, R. Kirsten, W. Roll, H.-H. of 4167 Hz and a pulse repetition of 6 sand 30° Brintzinger, S. Jiingling, R. Miilhaupt, and F. Lang pulse angle. Signals were assigned according to the hauser, Organometallics, 13, 964 (1994). literature.12,13 6. N. Herfert and G. Fink, Makromol. Chem., 193,1359 (1992). Melting points were determined by DSC from the 7. A. R. Siedle, W. M. Lamanna, J. M. Olofson, B. A. melting endotherm at a heating rate of 20 K/min Nerad, and R. A. Newmark, Selectivity in Catalysis, after previous heating to 185°C and cooling to 50°C M. E. Davis, S. L. Suib, Eds., ACS Symposium Series by 10 K/min. 517, Washington, DC, 1993, p. 156. Polymer molecular weight and molecular weight 8. Busico et. al. and Resconi et. al. recently reported a distribution were determined by size exclusion similar dependence of polypropylene tacticity on pro chromatography and viscosity measurements at the pene concentration for BI/MAO and Et(IndH4h polymer research division of BASF AG. ZrCldMAO. (a) V. Busico, lecture #1119, Milano, STEPOL 1994; (b) G. Balbontin, A. Fait, F. Piemon tesi, L. Resconi and H. Rychlicki, poster #40, Milano, This work was supported by the Bundesminister fiir STEPOL 1994. Forschung und Technologie (project #03M40719) and 9. M. Ystenes, Makromol. Chem. Macromol. Symp., 66, by BASF AG. We thank Witco AG for providing sam 71 (1993). ples of MAO and Dr. Lilge, BASF AG, for analytical 10. G. Hidalgo-Llinas, A. Munoz-Escalona, poster #54, assistance. Milano, STEPOL 1994. 1317 11. (a) D. Fischer and R. Miilhaupt, J. Organomet. Chem., 17. A. B. de Carvalho, P. E. Gloor, and A. E. Hamielec, 417, C7 (1991); (b) D. Fischer, Ph.D. thesis, Uni Polymer, 30,280 (1989). versity of Freiburg, 1992. 18. K. Soga, D. H. Lee and Y. Morikawa, Polymer, 33, 12. (a) A. Grassi, A. Zambelli, L. Resconi, E. Albizzati, 2408 (1992). and R. Mazzocchi, Macromolecules, 21,617 (1988); 19. U. Plocker, H. Knapp, and J. Prausnitz, Ind. Eng. (b) H. N. Cheng and J. A. Ewen, Makromol. Chem., Chem. Proc. Des. Dev., 17, 324 (1978). 190,1931 (1989); (c) B. Rieger, X. Mu, D. T. Mallin, 20. The smallest detectable intensity is ca. 0.05% of M. D. Rausch, and J. C. W. Chien, Macromolecules, the mmmm-signal under the described experimental 23, 3559 (1990); (d) T. Shiono, H. Kurosawa, O. conditions. For BIjMAO (run #103), a concentra Ishida, and K. Soga, Macromolecules, 26, 2085 (1993). tion of isopropyl end groups less than ca. 10% of 13. T. Tsutsui, N. Kashiwa, and A. Mizuno, Makromol. the n-butyl group concentration is, thus, not de Chem. Rapid Commun., 11,565 (1990). tectable. For MBIjMAO (run #104), isopropyl sig 14. B. Rieger, A. Reinmuth, W. Roll, and H.-H. Brint nals with intensity of less than 25% of the n-butyl zinger, J. Mol. Catal., 82,67 (1993). 15. (a) V. Busieo, R. Cipullo, and P. Corradini, Makromol. signals are not detectable due to the higher molec Chem. Macromol. Chem. Phys., 194,1079 (1993). (b) ular weight of this polymer. J. C. Chadwiek, A. Miedema and O. Sudmeijer, Macromol. Chem. Phys., 195, 167 (1994). 16. V. Busieo, R. Cipullo, and P. Corradini, Makromol. Chem. Rapid Commun., 14,97 (1993).